1. Field of the Invention
The present invention relates generally to magnetic specimens. More particularly, the present invention relates to examining or inspecting magnetic materials or devices.
2. Description of the Background Art
In recent years, the areal density of disk drives has increased by about 60% to 100% per year. This exponential increase is comparable to the increase in density of integrated circuit chips as described by Moore's law (predicting that the density of IC chips doubles about every 18 months). The areal density increases have been achieved by developing new materials for magnetic media and improving read/write heads.
As the technology of magnetic media and heads continue to advance, it is desirable to develop and improve techniques for inspecting or reviewing the magnetic media and/or heads. Conventional techniques for examining magnetic specimens include Lorentz microscopy and magnetic force microscopy.
Lorentz microscopy involves transmission of high energy electrons through thin samples of magnetic specimens. The magnetic contrast occurs due to the interaction of the electrons passing through the magnetic induction due to the magnetization of the specimen. Components of the magnetic induction normal to the electron beam cause deflection of the beam. A significant disadvantage of Lorentz microscopy is that it is applied to specimens thin enough for electron transmission. This typically requires substantial sample preparation that is often destructive of the specimen being examined.
Magnetic force microscopy (MFM) is a standard technique for investigating magnetic media. MFM uses a magnetic tip on a small cantilever to probe a magnetic field above a surface of a specimen. The magnetic field causes a force that deflects the cantilever. MFM does not require preparation of an electron thin sample. However, MFM has various limitations. In particular, MFM requires the entire area of interest to be scanned or translated under the magnetic tip. Hence, examining a relatively large area using MFM is a relatively slow process.
Another conventional technique for examining magnetic media involves writing and reading the media on a spin stand with a magnetic reader head. Such a technique is often used to screen heads and to characterize media. A further application is to recover lost data from hard disks by just reading the data with a flying head. For data recovery to succeed using the conventional technique the head must fly very low (of order 5-30 nm) over the spinning disk. This puts stringent demands on the flatness and perfection of the disk surface, for this method to be viable. For this reason a crashed or otherwise damaged disk is often not be recoverable in a disk drive or with a spin stand approach. An additional data recovery limitation is that the resolution is limited to that of the read head and one cannot image partially erased track fragments.